Are We Smart Enough to Know How Smart Animals Are?(28)

Inspired by an Aesop fable, crows have been tested to see if they will throw stones into a tube filled with water to bring floating rewards within reach. They do.

The Ancient Greek poet Aesop may have had an inkling of these talents given his fable The Crow and the Pitcher. “A Crow, half-dead with thirst,” so the fabulist went, “came upon a Pitcher.” There wasn’t enough water in the pitcher for the crow to be able to drink it. He tried to reach in with his beak, but the water level was too low. “Then a thought came to him,” as Aesop put it, “and he took a pebble and dropped it into the Pitcher.” Many more pebbles followed until the water had risen enough for a drink. It seems an unlikely feat, but it has now been replicated in the lab. The first was an experiment on rooks, a corvid that in the wild does not use any tools. The rooks were presented with a vertical water-filled tube with a floating mealworm just out of reach. The water level would have to be raised if the rook were to reach the delicacy. The same experiment was carried out with New Caledonian crows, known as real tool experts. True to the dictum that necessity is the mother of invention, and confirming Aesop’s story several millennia later, both crow species successfully solved the floating worm puzzle by using pebbles to raise the water level in the tube.39

Let me add some caution, though, because it is unclear how insightful this solution was. For one thing, all the birds had been pretrained using a slightly different task. They had received ample rewards for plunging stones into a tube. Moreover, while they were facing the tube with the mealworm, stones had been conveniently placed right next to it. The experimental setup strongly suggested the solution, therefore. Imagine that K?hler had taught his chimps to stack boxes! We would never have heard of him, as it would have undermined any claims of insight. In the course of testing, the crows did learn that large stones work better than small ones, and that there is no point dropping stones into a pipe filled with sawdust. Rather than working these answers out in their minds, however, it may have been a matter of fast learning. Perhaps they noticed that adding stones to water brought the mealworm closer, which led them to persist.40

When we recently presented our chimpanzees with a floating peanut task, a female named Liza solved it right away, adding water to a plastic tube. After some vigorous but ineffective kicking and shaking of the tube, Liza abruptly turned around, went to the drinker to fill her mouth, and returned to the tube to add water. She made several more trips to the drinker before she got the peanut at the right level to reach it with her fingers. Other chimps were less successful, but one female tried to pee into the tube! She had the right idea even though the execution was flawed. I have known Liza all her life and am sure that this problem was brand new to her.

Our experiment was inspired by a floating peanut task conducted on a large number of orangutans and chimpanzees, a subset of which cracked the puzzle at first sight.41 This is especially remarkable, since—unlike the crows—the apes had no pretraining; nor did they find any tools nearby. Rather, they must have conjured the effectiveness of water in their heads before going out of their way to collect it. Water doesn’t even look like a tool. How hard this task is became clear from tests on children, many of which never found the solution. Only 58 percent of eight-year-olds came up with it, and only 8 percent of four-year-olds. Most children frantically try to reach the prize with their fingers, then give up.42

These studies have set up a friendly rivalry between primate chauvinists and corvid aficionados. I sometimes teasingly accuse the latter of “ape envy,” because in every publication they draw a contrast with the primates, saying the corvids are either doing better or at least equally well. Calling their birds “feathered apes,” they make outrageous claims such as “The only credible evidence of technological evolution in nonhumans to date comes from New Caledonian crows.”43 Primatologists, on the other hand, wonder how generalizable corvid tool skills are, and if “feathered monkeys” isn’t a better moniker for the birds. Are crows one-trick ponies, like the clam-smashing otters or the Egyptian vultures that throw rocks at ostrich eggs? Or do they have the intelligence to take on a broad array of problems?44 This issue is far from settled, because even though ape intelligence has been studied for over a century, corvid tool studies have come up only in the last decade.

An intriguing new entry is the use of metatools by New Caledonian crows. A crow is presented with a piece of meat that it can retrieve only by using a long stick, but this stick is behind bars wide enough for the crow’s beak but not its head. The crow is unable to reach the tool. In a nearby box, however, lies a short stick suitable for retrieving the long one. To solve this problem, the right order is to pick up the short stick, use it to fetch the long one, and then apply the latter stick for the meat. The crow needs to understand that tools can be used on nonfood objects and to take steps in the right order. Alex Taylor and coworkers used wild New Caledonian crows on Maré Island, placed temporarily in an aviary. They tested seven crows, all of which managed metatool use; three followed the right sequence on the first attempt.45 Presently, Taylor is trying out tasks with even more steps, and the crows are keeping up with the challenge. This is most impressive, and considerably better than monkeys, which have trouble with stepwise tasks.

Given the evolutionary gulf between primates and corvids, and the many ancestral species of mammals and birds in between that don’t use tools, we are dealing with a typical example of convergent evolution. Independently, both taxonomic groups must have faced a need for complex manipulations of items in their environment, or other challenges that stimulated brain growth, which led them to evolve strikingly similar cognitive skills.46 The arrival of corvids on the scene illustrates how discoveries of mental life ripple across the animal kingdom, a process best summarized by what I’ll call my cognitive ripple rule: Every cognitive capacity that we discover is going to be older and more widespread than initially thought. This is rapidly becoming one of the best-supported tenets of evolutionary cognition.